Discharge-lamp lighting apparatus

ABSTRACT

A discharge-lamp lighting apparatus includes first and second cold cathode fluorescent lamps (CCFLs) and first and second transformers. The second transformer has a primary winding connected in parallel to one of primary and secondary windings of the first transformer, a first secondary winding, and a second secondary winding. Each of the first and second secondary windings of the second transformer is connected to the secondary winding of the first transformer with polarities being set so that a voltage of each secondary winding of the second transformer becomes additive to a voltage of the secondary winding of the first transformer. The first CCFL is connected in parallel to a series circuit that includes the secondary winding of the first transformer and the first secondary winding of the second transformer.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a discharge-lamp lightingapparatus for lighting discharge lamps such as cold cathode fluorescentlamps (CCFLs), and particularly, to a technique of simultaneouslydriving a plurality of CCFLs.

2. Description of the Related Art

FIG. 1 is a view showing a configuration of a discharge-lamp lightingapparatus according to a related art. This apparatus includes a DC powersource E connected in series with a first switching element Q1 and asecond switching element Q2. The first and second switching elements Q1and Q2 are turned on and off in response to control signals from acontrol circuit 10. The control circuit 10 conducts PWM control, phasecontrol, frequency control, or the like to control the on/off operationof the first and second switching elements Q1 and Q2.

The second switching element Q2 is connected in parallel to aquasi-voltage-resonance capacitor C6. The element Q2 is also connectedin parallel to a series circuit that includes a primary winding P1 of afirst transformer T1 and a current resonance capacitor C4. The firsttransformer T1 has a leakage inductance Lr for managing resonanceoperation.

A secondary winding S1 of the first transformer T1 is connected, througha resistor RS, in parallel to a series circuit that includes a coldcathode fluorescent lamp (hereinafter referred to as CCFL) 11 a and aballast capacitor C11 and a series circuit that includes a CCFL 11 b anda ballast capacitor C12. The resistor RS is a current detection resistorto detect a current. A signal representative of the current detected bythe resistor RS is fed back to the control circuit 10 on the primaryside. According to the signal fed back from the resistor RS, the controlcircuit 10 controls on/off operation of the first and second switchingelements Q1 and Q2, thereby controlling an AC voltage applied to theprimary winding P1 of the first transformer T1.

FIG. 2 shows a voltage-current characteristic of a typical CCFL. TheCCFL has a negative resistance characteristic that a current (lampcurrent) increases as an applied voltage (lamp voltage) decreases. Torelieve the negative resistance characteristic, an impedance element isinserted in series with a CCFL in the discharge-lamp lighting apparatus.The impedance element must have a sufficient value to absorb thenegative resistance characteristic of the CCFL. When driving a singleCCFL, the discharge-lamp lighting apparatus uses the leakage inductanceLr of the first transformer T1 as the impedance element.

When simultaneously driving a plurality of CCFLs, simply connecting theCCFLs in parallel with one another causes a problem that a CCFL that isfirst turned on triggers a voltage drop due to impedance to prevent theother CCFLs from being turned on. To avoid this problem, an impedanceelement is inserted in series with each CCFL. In the example shown inFIG. 1, the impedance elements are the ballast capacitors C11 and C12.With the ballast capacitors C11 and C12, a voltage applied to thesecondary winding S1 of the first transformer T1 becomes free from theON or OFF state of any CCFL, and therefore, all CCFLs are surely turnedon.

Another example of the discharge-lamp lighting apparatus is a multi-lampdrive system disclosed in Japanese Unexamined Patent ApplicationPublication No. 2003-31383. This multi-lamp drive system drives a lampset consisting of first and second lamps. The system includes a drivecircuit for converting a DC signal into an AC signal, a transformerwhose primary side is electrically connected to the driver circuit andwhose secondary side provides an AC power source, and a current balancecircuit electrically connected to the lamp set to balance currentspassed to the first and second lamps. The current balance circuit has acore, a first winding electrically connected to the first lamp, and asecond winding electrically connected to the second lamp. The first andsecond windings are wound around the same core and have the same numberof turns.

SUMMARY OF THE INVENTION

The discharge-lamp lighting apparatuses mentioned above have problems.In FIG. 1, the first transformer T1 must generate on its secondarywinding S1 a high voltage that is the sum of voltages applied to theballast capacitors C11 and C12 and voltages applied to the CCFLs 11 aand 11 b. Due to this, the apparatus must take large-scale safetymeasures to secure reliability, prevent leakage, and ensure creepagedistances and spatial distances. These measures increase the cost of theapparatus.

A discharge-lamp lighting apparatus of the present invention needs nolarge-scale safety measures, greatly reduces the cost, realizes highreliability, and accurately stabilizes and balances currents passed toCCFLs that are simultaneously driven.

According to a first aspect of the present invention, provided is adischarge-lamp lighting apparatus having a first discharge lamp and asecond discharge lamp. The apparatus includes a first transformer havinga primary winding and a secondary winding, the primary winding receivingan AC voltage generated by turning on/off switching elements connectedto a DC power source, the secondary winding transforming the AC voltagereceived by the primary winding into an output voltage; a secondtransformer having a primary winding, a first secondary winding, and asecond secondary winding, the primary winding of the second transformerbeing connected in parallel to one of the primary and secondary windingsof the first transformer, each of the first and second secondarywindings of the second transformer being connected to the secondarywinding of the first transformer with polarities being set so that avoltage of each secondary winding of the second transformer becomesadditive to a voltage of the secondary winding of the first transformer.The first discharge lamp is connected in parallel to a series circuitthat includes the secondary winding of the first transformer and thefirst secondary winding of the second transformer. The second dischargelamp is connected in parallel to a series circuit that includes thesecondary winding of the first transformer and the second secondarywinding of the second transformer.

According to a second aspect of the present invention, provided is adischarge-lamp lighting apparatus having a first discharge lamp and asecond discharge lamp. The apparatus includes a first transformer havinga primary winding and a secondary winding, the primary winding receivingan AC voltage generated by turning on/off switching elements connectedto a DC power source, the secondary winding transforming the AC voltagereceived by the primary winding into an output voltage; a secondtransformer having a primary winding and a secondary winding, theprimary winding of the second transformer being connected in parallel toone of the primary and secondary windings of the first transformer, thesecondary winding of the second transformer being connected to thesecondary winding of the first transformer with polarities being set sothat a voltage of the secondary winding of the second transformerbecomes additive to a voltage of the secondary winding of the firsttransformer; and a third transformer having a primary winding and asecondary winding, the primary winding of the third transformer beingconnected in parallel to one of the primary and secondary windings ofthe first transformer, the secondary winding of the third transformerbeing connected to the secondary winding of the first transformer withpolarities being set so that a voltage of the secondary winding of thethird transformer becomes additive to a voltage of the secondary windingof the first transformer. The first discharge lamp is connected inparallel to a series circuit that includes the secondary winding of thefirst transformer and the secondary winding of the second transformer.The second discharge lamp is connected in parallel to a series circuitthat includes the secondary winding of the first transformer and thesecondary winding of the third transformer.

According to a third aspect of the present invention, provided is adischarge-lamp lighting apparatus having a first discharge lamp and asecond discharge lamp. The apparatus includes a first transformer havinga primary winding and a secondary winding, the primary winding receivingan AC voltage generated by turning on/off switching elements connectedto a DC power source, the secondary winding transforming the AC voltagereceived by the primary winding into an output voltage; a secondtransformer having a primary winding and a secondary winding, theprimary winding of the second transformer being connected in parallel toone of the primary and secondary windings of the first transformer, thesecondary winding of the second transformer being connected to thesecondary winding of the first transformer with polarities being set sothat a voltage of the secondary winding of the second transformerbecomes additive to a voltage of the secondary winding of the firsttransformer; and a third transformer having a primary winding and asecondary winding, the primary winding of the third transformer beingconnected in series with the primary winding of the second transformer,the secondary winding of the third transformer being connected to thesecondary winding of the first transformer with polarities being set sothat a voltage of the secondary winding of the third transformer becomesadditive to a voltage of the secondary winding of the first transformer.The first discharge lamp is connected in parallel to a series circuitthat includes the secondary winding of the first transformer and thesecondary winding of the second transformer. The second discharge lampis connected in parallel to a series circuit that includes the secondarywinding of the first transformer and the secondary winding of the thirdtransformer.

According to a first aspect of the present invention, provided is adischarge-lamp lighting apparatus having a first discharge lamp and asecond discharge lamp. The apparatus includes a first transformer havinga primary winding and a secondary winding, the primary winding receivingan AC voltage generated by turning on/off switching elements connectedto a DC power source, the secondary winding transforming the AC voltagereceived by the primary winding into an output voltage; and a secondtransformer having a primary winding, a first secondary winding, and asecond secondary winding, the primary winding of the second transformerbeing connected in series with one of the primary and secondary windingsof the first transformer, each of the first and second secondarywindings of the second transformer being connected to the secondarywinding of the first transformer with polarities being set so that avoltage of each secondary winding of the second transformer becomesadditive to a voltage of the secondary winding of the first transformer.The first discharge lamp is connected in parallel to a series circuitthat includes the secondary winding of the first transformer and thefirst secondary winding of the second transformer. The second dischargelamp is connected in parallel to a series circuit that includes thesecondary winding of the first transformer and the second secondarywinding of the second transformer.

According to a fifth aspect of the present invention, provided is adischarge-lamp lighting apparatus having a first discharge lamp and asecond discharge lamp. The apparatus includes a first transformer havinga primary winding and a secondary winding, the primary winding receivingan AC voltage generated by turning on/off switching elements connectedto a DC power source, the secondary winding transforming the AC voltagereceived by the primary winding into an output voltage; a secondtransformer having a primary winding and a secondary winding, theprimary winding of the second transformer being connected in series withone of the primary and secondary windings of the first transformer, thesecondary winding of the second transformer being connected to thesecondary winding of the first transformer with polarities being set sothat a voltage of the secondary winding of the second transformerbecomes additive to a voltage of the secondary winding of the firsttransformer; and a third transformer having a primary winding and asecondary winding, the primary winding of the third transformer beingconnected in series with one of the primary and secondary windings ofthe first transformer, the secondary winding of the third transformerbeing connected to the secondary winding of the first transformer withpolarities being set so that a voltage of the secondary winding of thethird transformer becomes additive to a voltage of the secondary windingof the first transformer. The first discharge lamp is connected inparallel to a series circuit that includes the secondary winding of thefirst transformer and the secondary winding of the second transformer.The second discharge lamp is connected in parallel to a series circuitthat includes the secondary winding of the first transformer and thesecondary winding of the third transformer.

According to a sixth aspect of the present invention, provided is adischarge-lamp lighting apparatus having a first discharge lamp and asecond discharge lamp. The apparatus includes a first transformer havinga primary winding and a secondary winding, the primary winding receivingan AC voltage generated by turning on/off switching elements connectedto a DC power source, the secondary winding transforming the AC voltagereceived by the primary winding into an output voltage; a secondtransformer having a primary winding and a secondary winding, theprimary winding of the second transformer being connected in series withone of the primary and secondary windings of the first transformer, thesecondary winding of the second transformer being connected to thesecondary winding of the first transformer with polarities being set sothat a voltage of the secondary winding of the second transformerbecomes additive to a voltage of the secondary winding of the firsttransformer; and a third transformer having a primary winding and asecondary winding, the primary winding of the third transformer beingconnected in series with the primary winding of the second transformer,the secondary winding of the third transformer being connected to thesecondary winding of the first transformer with polarities being set sothat a voltage of the secondary winding of the third transformer becomesadditive to a voltage of the secondary winding of the first transformer.The first discharge lamp is connected in parallel to a series circuitthat includes the secondary winding of the first transformer and thesecondary winding of the second transformer. The second discharge lampis connected in parallel to a series circuit that includes the secondarywinding of the first transformer and the secondary winding of the thirdtransformer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing a configuration of a discharge-lamp lightingapparatus according to a related art;

FIG. 2 is a view showing a voltage-current characteristic of a typicalCCFL;

FIG. 3 is a view showing a configuration of a discharge-lamp lightingapparatus according to first embodiment of the present invention;

FIG. 4 is a view showing a configuration of a discharge-lamp lightingapparatus according to second embodiment of the present invention;

FIG. 5 is a view showing a configuration of a discharge-lamp lightingapparatus according to third embodiment of the present invention;

FIG. 6 is a view showing a configuration of a discharge-lamp lightingapparatus according to fourth embodiment of the present invention;

FIG. 7 is a view showing a configuration of a discharge-lamp lightingapparatus according to fifth embodiment of the present invention;

FIG. 8 is a view showing a configuration of a discharge-lamp lightingapparatus according to sixth embodiment of the present invention;

FIG. 9 is a view showing a configuration of a discharge-lamp lightingapparatus according to seventh embodiment of the present invention; and

FIG. 10 is a view showing a configuration of a discharge-lamp lightingapparatus according to eighth embodiment of the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

Discharge-lamp lighting apparatuses according to embodiments of thepresent invention will be explained in detail with reference to theaccompanying drawings.

First Embodiment

FIG. 3 is a view showing a discharge-lamp lighting apparatus accordingto first embodiment of the present invention. The operation andconfiguration of the primary side of first embodiment are the same asthose of the related art shown in FIG. 1, and therefore, explanationsthereof are omitted. In FIG. 3, the control circuit 10 and currentdetection resistor RS are not shown.

Parts of first embodiment that are different from those of the relatedart will mainly be explained. Through the drawings, a filled circleindicates a winding start point of each transformer winding. Althoughdischarge lamps in the embodiments are CCFLs, they may be externalelectrode fluorescent lamps, fluorescent lamps, and the like.

On the secondary side of the apparatus, there is a second transformer T2instead of the first and second ballast capacitors C11 and C12 of therelated art. The second transformer T2 has a primary winding P2, a firstsecondary winding S21, and a second secondary winding S22. The threewindings of the second transformer T2 are wound in order of S21, P2, andS22. The primary winding P2 and first secondary winding S21 of thesecond transformer T2 are loosely coupled to each other, the primarywinding P2 and second secondary winding S22 of the second transformer T2are loosely coupled to each other, and the first and second secondarywindings S21 and S22 of the second transformer T2 are loosely coupled toeach other.

A secondary winding S1 of a first transformer T1 is connected inparallel to a series circuit that includes a CCFL 11 a and the firstsecondary winding S21 of the second transformer T2 and a series circuitthat includes a CCFL 11 b and the second secondary winding S22 of thesecond transformer T2. The primary winding P2 of the second transformerT2 is connected in parallel to a primary winding P1 of the firsttransformer T1. Polarities of the first and second secondary windingsS21 and S22 of the second transformer T2 are set so that voltagesgenerated by the first and second secondary windings S21 and S22 areadditive to a voltage generated by the secondary winding S1 of the firsttransformer T1.

Operation of the discharge-lamp lighting apparatus according to firstembodiment with the above-mentioned configuration will be explained. AnAC voltage applied to the primary winding P1 of the first transformer T1and the primary winding P2 of the second transformer T2 makes thesecondary winding S1 of the first transformer T1 and the first andsecond secondary windings S21 and S22 of the second transformer T2generate voltages. As a result, the CCFL 11 a receives the sum of thevoltage of the secondary winding S1 of the first transformer T1 and thevoltage of the first secondary winding S21 of the second transformer T2,and the CCFL 11 b receives the sum of the voltage of the secondarywinding S1 of the first transformer T1 and the voltage of the secondsecondary winding S22 of the second transformer T2.

As a result, the CCFLs 11 a and 11 b turn on. Since the first and secondsecondary windings S21 and S22 of the second transformer T2 are looselycoupled to each other, ON operation of one of the CCFLs 11 a and 11 b donot drop a voltage applied to the other CCFL. Namely, the CCFLs 11 a and11 b can stably be turned on without an influence of voltage drop causedby ON operation of the CCFLs 11 a and 11 b.

The loose coupling of the primary winding P2 and first secondary windingS21 of the second transformer T2 forms a leakage inductance Lr1, and theloose coupling of the primary winding P2 and second secondary windingS22 of the second transformer T2 forms a leakage inductance Lr2. Theseleakage inductances result in balancing currents passed to the CCFLs 11a and 11 b. The voltages applied to the CCFLs 11 a and 11 b are sharedbetween the first and second transformers T1 and T2, and therefore, anoutput voltage provided by any one of the first and second transformersT1 and T2 can be lower than that of the related art. This results ineliminating the need of large-scale safety measures to securereliability, prevent leakage, and ensure creepage distances and spatialdistances, thereby minimizing the cost of the apparatus.

Second Embodiment

FIG. 4 is a view showing a configuration of a discharge-lamp lightingapparatus according to second embodiment of the present invention. Theprimary winding P2 of the second transformer T2 of the discharge-lamplighting apparatus according to the first embodiment is connected inparallel to the secondary winding S1 of the first transformer T1. Thedischarge-lamp lighting apparatus according to the present embodimentprovides the same operation and effect as the discharge-lamp lightingapparatus according to the first embodiment.

Third Embodiment

FIG. 5 is a view showing a configuration of a discharge-lamp lightingapparatus according to third embodiment of the present invention. Thesecond transformer T2 of the discharge-lamplighting apparatus accordingto the first embodiment is divided into a second transformer T2 and athird transformer T3. The second transformer T2 has a primary winding P2and a secondary winding S2, and the third transformer T3 has a primarywinding P3 and a secondary winding S3.

According to the third embodiment shown in FIG. 5, a secondary windingS1 of a first transformer T1 is connected in parallel to a seriescircuit that includes a CCFL 11 a and the secondary winding S2 of thesecond transformer T2 and a series circuit that includes a CCFL 11 b andthe secondary winding S3 of the third transformer T2. Each of theprimary windings P2 and P3 of the second and third transformers T2 andT3 is connected in parallel to the primary winding P1 of the firsttransformer T1. The secondary windings S2 and S3 of the second and thirdtransformers T2 and T3 are connected to the secondary winding S1 of thefirst transformer T1 with their polarities being set so that voltagesgenerated by the secondary windings S2 and S3 become additive to avoltage generated by the secondary winding S1 of the first transformerT1.

The primary and secondary windings P2 and S2 of the second transformerT2 are loosely coupled to each other, and the primary and secondarywindings P3 and S3 of the third transformer T3 are also loosely coupledto each other.

Operation of the discharge-lamp lighting apparatus according to thethird embodiment with the above-mentioned configuration will beexplained. An AC voltage applied to the primary windings P1, P2, and P3of the first, second, and third transformers T1, T2, and T3 makes thesecondary windings S1, S2, and S3 of the first, second, and thirdtransformers T1, T2, and T3 generate voltages. As a result, the CCFL 11a receives the sum of the voltage of the secondary winding S1 of thefirst transformer T1 and the voltage of the secondary winding S2 of thesecond transformer T2.

Similarly, the CCFL 11 b receives the sum of the voltage of thesecondary winding S1 of the first transformer T1 and the voltage of thesecondary winding S3 of the third transformer T3.

As a result, the CCFLs 11 a and 11 b turn on. Since the secondarywindings S2 and S3 of the second and third transformers T2 and T3 areindependent of each other, ON operation of one of the CCFLs 11 a and 11b do not drop a voltage applied to the other CCFL. Namely, the CCFLs 11a and 11 b can stably be turned on without an influence of voltage dropcaused by ON operation of the CCFLs 11 a and 11 b.

The loose coupling of the primary and secondary windings P2 and S2 ofthe second transformer T2 forms a leakage inductance Lr1, and the loosecoupling of the primary and secondary windings P3 and S3 of the thirdtransformer T3 forms a leakage inductance Lr2. These leakage inductancesresult in balancing currents passed to the CCFLs 11 a and 11 b. Thevoltages applied to the CCFLs 11 a and 11 b are shared between the firstand second transformers T1 and T2 and between the first and thirdtransformers T1 and T3, and therefore, an output voltage provided by anyone of the first to third transformers T1 to T3 can be lower than thatof the related art. This results in eliminating the need of large-scalesafety measures to secure reliability, prevent leakage, and ensurecreepage distances and spatial distances, thereby minimizing the cost ofthe apparatus.

Fourth Embodiment

FIG. 6 is a view showing a configuration of a discharge-lamp lightingapparatus according to fourth embodiment of the present invention. Eachof the primary windings P2 and P3 of the second and third transformersT2 and T3 of the discharge-lamp lighting apparatus of the thirdembodiment is connected in parallel to the secondary winding S1 of thefirst transformer T1. The fourth embodiment provides the same operationand effect as the third embodiment.

Fifth Embodiment

FIG. 7 is a view showing a configuration of a discharge-lamp lightingapparatus according to fifth embodiment of the present invention. Theprimary windings P2 and P3 of the second and third transformers T2 andT3 of the discharge-lamp lighting apparatus of the third embodiment isconnected in series with each other to form a series circuit and thisseries circuit is connected in parallel to the primary winding P1 of thefirst transformer T1 of the third embodiment. The fifth embodimentprovides the same operation and effect as the third embodiment.

Like the fourth embodiment, the fifth embodiment may be modified toconnect the above-mentioned series circuit in parallel to the secondarywinding S1 of the first transformer T1. The modification provides thesame operation and effect as the fifth embodiment.

Sixth Embodiment

FIG. 8 is a view showing a configuration of a discharge-lamp lightingapparatus according to sixth embodiment of the present invention.

The primary winding P2 of the second transformer T2 of thedischarge-lamp lighting apparatus of first embodiment is connected inseries with the primary winding P1 of the first transformer T1. Thesixth embodiment provides the same operation and effect as the firstembodiment.

Like the second embodiment, the sixth embodiment may be modified toconnect the primary winding P2 of the second transformer T2 in serieswith the secondary winding S1 of the first transformer T1. Thismodification provides the same operation and effect as the secondembodiment.

Seventh Embodiment

FIG. 9 is a view showing a configuration of a discharge-lamp lightingapparatus according to seventh embodiment of the present invention. Eachof the primary windings P2 and P3 of the second and third transformersT2 and T3 of the discharge-lamp lighting apparatus of the thirdembodiment is connected in series with the primary winding P1 of thefirst transformer T1. The seventh embodiment provides the same operationand effect as the third embodiment.

Like the fourth embodiment, the seventh embodiment may be modified toconnect each of the primary windings P2 and P3 of the second and thirdtransformers T2 and T3 in series with the secondary winding S1 of thefirst transformer T1. This modification provides the same operation andeffect as the fourth embodiment.

Eighth Embodiment

FIG. 10 is a view showing a discharge-lamp lighting apparatus accordingeighth embodiment of the present invention.

The primary windings P2 and P3 of the second and third transformers T2and T3 of the discharge-lamp lighting apparatus of third embodiment isconnected in series with each other to form a series circuit and thisseries circuit is connected in series with the primary winding P1 of thefirst transformer T1. The eighth embodiment provides the same operationand effect as the third embodiment.

Like the fourth embodiment, the eighth embodiment may be modified toconnect the series circuit consisting of the primary windings P2 and P3of the second and third transformers T2 and T3 in series with thesecondary winding S1 of the first transformer T1. This modificationprovides the same operation and effect as the eighth embodiment.

Although each of the first embodiment to the eighth embodiment controlstwo CCFLs, the present invention is applicable to form a discharge-lamplighting apparatus that controls an optional number of CCFLs.

The present invention can realize a discharge-lamp lighting apparatusthat is manufacturable at low cost, is highly reliable, and is capableof simultaneously driving a plurality of CCFLs.

The discharge-lamp lighting apparatus according to the present inventiongenerates voltages applied to first and second discharge lamps fromfirst and second (and third, too) transformers in a shared manner toreduce a voltage to be generated by each transformer. This results ineliminating large-scale safety measures to be taken for the apparatus,greatly reducing the cost of the apparatus, and improving thereliability of the apparatus.

Supplying voltages to the first and second discharge lamps with the useof the second and/or third transformers provides an advantage that aleakage inductance of each transformer can be used as an impedance toabsorb the negative resistance characteristics of the first and seconddischarge lamps. This results in stabilizing and balancing currentspassed to the discharge lamps that are simultaneously driven.

This application claims benefit of priority under 35 USC §119 toJapanese Patent Application No. 2006-145730, filed on May 25, 2006, theentire contents of which are incorporated by reference herein. Althoughthe invention has been described above by reference to certainembodiments of the invention, the invention is not limited to theembodiments described above. Modifications and variations of theembodiments described above will occur to those skilled in the art, inlight of the teachings. The scope of the invention is defined withreference to the following claims.

1. A discharge-lamp lighting apparatus having a first discharge lamp anda second discharge lamp, comprising: a first transformer having aprimary winding and a secondary winding, the primary winding receivingan AC voltage generated by turning on/off switching elements that areconnected to a DC power source, and the secondary winding transformingthe AC voltage received by the primary winding into an output voltage;and a second transformer having a primary winding, a first secondarywinding, and a second secondary winding, the primary winding of thesecond transformer being driven in synchronization with the firsttransformer, and each of the first and second secondary windings of thesecond transformer being connected to the secondary winding of the firsttransformer with polarities being set so that a voltage of eachsecondary winding of the second transformer becomes additive to avoltage of the secondary winding of the first transformer, wherein thefirst discharge lamp is connected in parallel to a series circuit thatincludes the secondary winding of the first transformer and the firstsecondary winding of the second transformer; and the second dischargelamp is connected in parallel to a series circuit that includes thesecondary winding of the first transformer and the second secondarywinding of the second transformer.
 2. A discharge-lamp lightingapparatus of claim 1, wherein the primary winding of the secondtransformer is connected in parallel to the primary winding of the firsttransformer.
 3. A discharge-lamp lighting apparatus of claim 1, whereinthe primary winding of the second transformer is connected in parallelto the secondary winding of the first transformer.
 4. A discharge-lamplighting apparatus according to claim 1, wherein the primary winding ofthe second transformer is connected in series with the primary windingsof the first transformer.
 5. A discharge-lamp lighting apparatus ofclaim 1, wherein the primary winding and the first secondary winding ofthe second transformer are loosely coupled to each other; the primarywinding and the second secondary winding of the second transformer areloosely coupled to each other; the first secondary winding and thesecond secondary winding of the second transformer are loosely coupledto each other.